If you and your competitors have equally old domain names that are qually aged and equally trusted then it comes down to PR. PR is neither useless or entireably reliable, people who are saying extreme things are wrong here imo.
After so long--I find a like minded buddy here I don't know why people downplay PR for SERPs ranking. While it is irrelevant for MSN, Yahoo ranking -- I would ask anybody --who does not think PR is important for serps --to type any keyword/keyphrase --on Google and then check PR of first 100 sites. Hardly 10-15 sites will be bellow PR4 --or less. So what does it mean??? It means PR is highly important for SERPs on Google. And MSN or Yahoo hardly bring any traffic--it is the big-daddy that is all about traffic.
I think PR now has less value but for other sites that is looking for link exchange they check the PR of the site. If you get high PR other sites might be interested to link exchange with your site. But PR don't have any effect to your site SERP.
PR is not that important unless you are going for competitive keywords. Even then it is not everything. For example, a highly competitive search phrase 'used cars' gives these results: Position 1: PR6 2: PR7 3: PR8 4: PR7 5: PR6 Whereas a search for a more uncommon phrase 'orange cats' gives: 1: PR2 2: PR4 3: PR6 4: PR3 5: PR5 For the competitive search you can see that a PR4 or less would never make it to the top 10, whereas nearly anything goes for weaker, long-tail type searches.
Good PR is very important for the long term. It might not mean high traffic but it means you have quality related backlinks which is good for ranking high in search engines.
PR is just part of what google uses to figure out SERP. It's good to have and helps your results but is not the do all end all.